1. Field of the Invention
The present invention relates to a machine used to stretch, or tenter, a fabric, web or film in a direction transverse to that in which it is being conveyed through a treatment zone, such as a process oven, or to prevent the fabric, web or film from shrinking in a transverse direction as it is being conveyed through such a zone. Specifically, the present invention is a tentering machine which includes means for reducing or eliminating longitudinal distortion during tentered processing.
2. Description of the Prior Art
Tentering machines are well known in the art. Generally, these machines include pin-plates or clamps which grasp the opposite edges of the fabric, web or film to be stretched in a widthwise, or transverse direction, or to prevent their shrinking in such a direction.
The pin-plates or clamps may convey the fabric through a stretching, or tentering, zone, where they, while grasping opposite edges of the fabric, are conveyed along divergent tracks. Both before and after the tentering zone, the pin-plates or clamps on opposite sides of the fabric may proceed in parallel directions. Alternatively, the pin-plates or clamps may be conveyed only along parallel tracks so that they may prevent shrinkage from occurring in a treatment zone.
The pin-plates or clamps are driven about a pair of endless-loop paths which are adjacent to and face one another. In the tentering machines of the prior art, they are commonly attached firmly to a drive chain, which may describe an endless-loop path within that followed by the pin plates or clamps.
The tentering zone, then, is between the pair of endless-loop paths around which the pin-plates or clamps are conveyed. Initially, those on each endless-loop path grasp the opposite edges of the fabric to be tentered and may be conveyed in directions parallel to one another. In the tentering zone, they may proceed along divergent paths stretching the fabric in a widthwise direction while conveying the fabric longitudinally therethrough, or they may remain travelling in parallel directions simply to prevent shrinkage. Finally, upon exiting from the tentering zone, they may again be conveyed in directions parallel to one another, if they have diverged, before releasing the fabric.
If the fabric, web or film elongates in a direction parallel to its motion while tentered, the rigid spacing between adjacent pin-plates or clamps in prior-art tentering machines, where they are firmly attached to the drive chain, may permit distortion. Some manufacturers have attempted to overcome this disadvantage by attaching the pin-plates or clamps to the drive chain using drive pins in slotted holes, but this limits the web elongation to the length of the slot. In addition, web driving force is lost when the drive pin leaves the end of the slot.
Other manufacturers have added springs to the drive slot to maintain drive force, but such an expedient limits web elongation even more seriously.
The present invention supplies a solution to these disadvantages in the tentering machines of the prior art by including means whereby pin-plates or clamps may be driven from a chain in a manner which permits considerable web elongation without loss of driving force. In addition, the means of the present invention permits the direction of motion of the entire line to be reversed without modification or loss of function.